Characteristics of the stress relaxation in the thinned two-phase multilayer materials

In the two-phase multilayer bulk material, strong inner stress field may exist if the thermal expansion coefficient of one phase is distinctly different from that of another phase. When a sample is thinned in cross section of the bulk material for studying by transmission electron microscopy (TEM), stress relaxation will occur in the sample. Thus, stress and strain states in the sample are different from that in the bulk material. In this paper, the finite element method was employed to analyze the characteristics about stress relaxation in the sample when the sample was separated from the bulk material. Results show that: larger residual stresses still remain near the interface; the shear stress field is formed at the local interface region near the free surface, and; stresses change drastically near the intersection of interface and free surface. When the ratio of the sample thickness to the layer thickness is small, the stress σzz (perpendicular to the sample surface) relaxes throughout the sample thickness in the region remote from the interface, and this stress remains only near the interface. When the ratio of the sample thickness to the layer thickness is large, stress relaxation occurs only near the free surface.